Method to enhance phosphor robustness and dispersability and resulting phosphors

ABSTRACT

Briefly, in one aspect, the present invention relates to processes for producing a stabilized Mn4+ doped phosphor in solid form and a composition containing such doped phosphor. Such process may include combining a) a solution comprising at least one substance selected from the group consisting of: K2HPO4, an aluminum phosphate, oxalic acid, phosphoric acid, a surfactant, a chelating agent, or a combination thereof, with b) a Mn4+ doped phosphor of formula I in solid form, where formula I may be: Ax [MFy]:Mn4+. The process can further include isolating the stabilized Mn4+ doped phosphor in solid form. In formula I, A may be Li, Na, K, Rb, Cs, or a combination thereof. In formula I, M may be Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or a combination thereof. In formula I, x is the absolute value of the charge of the [MFy] ion and y is 5, 6 or 7.

BACKGROUND

Red-emitting phosphors based on complex fluoride materials activated byMn⁴⁺, such as those described in U.S. Pat. Nos. 7,358,542, 7,497,973,and 7,648,649, can be utilized in combination with yellow/green emittingphosphors such as YAG:Ce to achieve warm white light (CCTs<5000 K on theblackbody locus, color rendering index (CRI)>80) from a blue lightemitting diode (LED), equivalent to that produced by currentfluorescent, incandescent and halogen lamps. These materials absorb bluelight strongly and efficiently emit in a range between about 610 nm and658 nm with little deep red/NIR emission. Therefore, luminous efficacyis maximized compared to red phosphors that have significant emission inthe deeper red where eye sensitivity is poor. Quantum efficiency canexceed 85% under blue (440-460 nm) excitation. In addition, use of thered phosphors for displays can yield high gamut and efficiency.

Processes for preparing Mn⁴⁺ doped complex fluoride phosphors withimproved color stability are described in U.S. Pat. No. 8,906,724 andother patents and patent applications assigned to General ElectricCompany or Current. Yet there remains a need for even furtherimprovements in stability and dispersibility of the complex fluoridephosphors, while maintaining excellent performance in lighting anddisplay applications.

BRIEF DESCRIPTION

Briefly, in one aspect, the present invention relates to a process forproducing a stabilized Mn⁺⁴ doped phosphor in solid form. Such processmay include combining a) a solution comprising at least one substanceselected from the group consisting of: K₂HPO₄, an aluminum phosphate,oxalic acid, phosphoric acid, a surfactant, a chelating agent, or acombination thereof, with b) a Mn⁺⁴ doped phosphor of formula I in solidform, where formula I may be: A_(x) [MF_(y)]:Mn⁺⁴. The process canfurther include isolating the stabilized Mn⁴⁺ doped phosphor in solidform. In formula I, A may be Li, Na, K, Rb, Cs, or a combinationthereof. In formula I, M may be Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y,La, Nb, Ta, Bi, Gd, or a combination thereof. In formula I, x is theabsolute value of the charge of the [MF_(y)] ion and y is 5, 6 or 7.

Another aspect of the present invention relates to a composition whichincludes a) at least one substance selected from the group consistingof: K₂HPO₄, an aluminum phosphate, oxalic acid, phosphoric acid, or acombination thereof, and b) a Mn⁴⁺ doped phosphor of formula I, whereformula I is: A_(x) [MF_(y)]:Mn⁴⁺. In formula I, A may be Li, Na, K, Rb,Cs, or a combination thereof. In formula I, M may be Si, Ge, Sn, Ti, Zr,Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or a combination thereof. Informula I, x is the absolute value of the charge of the [MF_(y)] ion andy is 5, 6 or 7.

Yet another aspect of the present invention is directed to a phosphorcomposition including phosphor particles and, on their surfaces, atleast one surface composition selected from the group consisting of: 1)a composition including a phosphorus-containing moiety and acarbon-containing moiety; 2) a composition including aphosphorus-containing moiety and a metal fluoride; 3) a compositionincluding a phosphorus-containing moiety and a carbon-containing moietyand a metal fluoride; and 4) a composition comprising thephosphorus-containing moiety free of an alkyl phosphate compound, wherethe phosphor particles comprise a Mn⁴⁺ doped phosphor of formula I;

A_(x)[MF_(y)]:Mn⁴⁺

where A is Li, Na, K, Rb, Cs, or a combination thereof,M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or acombination thereof,x is the absolute value of the charge of the [MF_(y)] ion; y is 5, 6 or7.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic cross-sectional view of a LED package inaccordance with one embodiment of the invention;

FIG. 2 is a schematic cross-sectional view of a LED package inaccordance with another embodiment of the invention;

FIG. 3 is a schematic cross-sectional view of a LED package inaccordance with yet another embodiment of the invention;

FIG. 4 is a cutaway side perspective view of a LED package in accordancewith one embodiment of the invention;

FIG. 5 is a schematic perspective view of a surface-mounted device (SMD)backlight LED.

FIG. 6 illustrates a backlight unit or module.

FIG. 7 illustrates a backlight unit or module.

DETAILED DESCRIPTION

In one aspect, the present invention relates to processes for producinga stabilized Mn⁴⁺ doped phosphor in solid form. Such processes mayinclude combining a) a solution including at least one substanceselected from the group consisting of: K₂HPO₄, an aluminum phosphate,oxalic acid, phosphoric acid, a surfactant, a chelating agent, or acombination thereof, with b) a Mn⁴⁺ doped phosphor of formula I in solidform. In an embodiment, the amount of the substance mentioned above is0.01-20% by weight relative to the amount of the Mn⁴⁺ doped phosphor offormula I, such as 1% to 15%, and 2% to 10%.

In another aspect the present invention relates to a composition whichincludes a) at least one substance selected from the group consistingof: K₂HPO₄, an aluminum phosphate, oxalic acid, phosphoric acid, asurfactant, a chelating agent, or a combination thereof, and b) a Mn⁴⁺doped phosphor of formula I.

The Mn⁴⁺ doped phosphors of formula I are complex fluoride materials, orcoordination compounds, containing at least one coordination centersurrounded by fluoride ions acting as ligands, and charge-compensated bycounter ions as necessary. For example, in K₂SiF₆:Mn⁴⁺, the coordinationcenter is Si and the counterion is K. Complex fluorides are occasionallywritten as a combination of simple, binary fluorides but such arepresentation does not indicate the coordination number for the ligandsaround the coordination center. The square brackets (occasionallyomitted for simplicity) indicate that the complex ion they encompass isa new chemical species, different from the simple fluoride ion. Theactivator ion (Mn⁴⁺) also acts as a coordination center, substitutingpart of the centers of the host lattice, for example, Si. The hostlattice (including the counter ions) may further modify the excitationand emission properties of the activator ion.

In particular embodiments, the coordination center of the phosphor, thatis, M in formula I, is Si, Ge, Sn, Ti, Zr, or a combination thereof.More particularly, the coordination center may be Si, Ge, Ti, or acombination thereof. The counterion, or A in formula I, may be Na, K,Rb, Cs, or a combination thereof, more particularly K. Examples ofphosphors of formula I include K₂[SiF₆]:Mn⁴⁺, K₂[TiF₆]:Mn⁴⁺,K₂[SnF₆]:Mn⁴⁺, Cs₂[TiF₆]:Mn⁴⁺, Rb₂[TiF₆] Mn⁴⁺, Cs₂[SiF₆]:Mn⁴⁺,Rb₂[SiF₆]:Mn⁴⁺, Na₂[TiF₆]:Mn⁴⁺, Na₂[ZrF₆]:Mn⁴⁺, K₃[ZrF₇]:Mn⁴⁺,K₃[BiF₆]:Mn⁴⁺, K₃[YF₆]:Mn⁴⁺, K₃[LaF₆]:Mn⁴⁺, K₃[GdF₆]:Mn⁴⁺,K₃[NbF₇]:Mn⁴⁺, K₃[TaF₇]:Mn⁴⁺. In particular embodiments, the phosphor offormula I is K₂SiF₆:Mn⁴⁺.

The amount of manganese in the Mn⁴⁺ doped phosphors of formula I mayrange from about 1.2 mol % based on the total number of moles of Mn andM (such as Si) (about 0.3 wt % based on total phosphor weight) to about21 mol % (about 5.1 wt %), particularly from about 1.2 mol % (about 0.3wt %) to about 16.5 mol % (about 4 wt %). In particular embodiments, theamount of manganese may range from about 2 mol % (about 0.5 wt %) to13.4 mol % (about 3.3 wt %), or from about 2 mol % to 12.2 mol % (about3 wt %), or from about 2 mol % to 11.2 mol % (about 2.76 wt %), or fromabout 2 mol % to about 10 mol % (about 2.5 wt %), or from about 2 mol %to 5.5 mol % (about 1.4 wt %), or from about 2 mol % to about 3.0 mol %(about 0.75 wt %).

The Mn⁴⁺ doped phosphor of formula I may be annealed to improvestability as described in U.S. Pat. No. 8,906,724 prior to combinationwith K₂HPO₄, an aluminum phosphate, oxalic acid, phosphoric acid, asurfactant, a chelating agent, or a combination thereof. In suchembodiments, the product phosphor is held at an elevated temperature,while in contact with an atmosphere containing a fluorine-containingoxidizing agent. The fluorine-containing oxidizing agent may be F₂, HF,SF₆, BrF₅, NH₄HF₂, NH₄F, KF, AlF₃, SbF₅, ClF₃, BrF₃, KrF₂, XeF₂, XeF₄,XeF₆, NF₃, SiF₄, PbF₂, ZnF₂, SnF₂, CdF₂, a C₁-C₄ fluorocarbon, or acombination thereof. Examples of suitable fluorocarbons include CF₄,C₂F₆, C₃F₈, CHF₃, CF₃CH₂F, and CF₂CHF. In particular embodiments, thefluorine-containing oxidizing agent is F₂. The amount of oxidizing agentin the atmosphere may be varied to obtain a color stable phosphor,particularly in conjunction with variation of time and temperature.Where the fluorine-containing oxidizing agent is F₂, the atmosphere mayinclude at least 0.5% F₂, although a lower concentration may beeffective in some embodiments. In particular the atmosphere may includeat least 5% F₂ and more particularly at least 20% F₂. The atmosphere mayadditionally include nitrogen, helium, neon, argon, krypton, xenon, inany combination with the fluorine-containing oxidizing agent. Inparticular embodiments, the atmosphere is composed of about 20% F₂ andabout 80% nitrogen.

The temperature at which the phosphor is contacted with thefluorine-containing oxidizing agent at an elevated temperature may be atemperature in the range from about 200° C. to about 700° C.,particularly from about 350° C. to about 600° C. during contact, and insome embodiments from about 500° C. to about 600° C. The phosphor iscontacted with the oxidizing agent for a period of time sufficient toconvert it to a color stable phosphor. Time and temperature areinterrelated, and may be adjusted together, for example, increasing timewhile reducing temperature, or increasing temperature while reducingtime. In particular embodiments, the time is at least one hour,particularly at least four hours, more particularly at least six hours,and most particularly at least eight hours. After holding at theelevated temperature for the desired period of time, the temperature inthe furnace may be reduced at a controlled rate while maintaining theoxidizing atmosphere for an initial cooling period. The temperature maybe reduced to about 200° C. with controlled cooling, then control may bediscontinued if desired.

The manner of contacting the phosphor with the fluorine-containingoxidizing agent is not critical and may be accomplished in any waysufficient to convert the phosphor to a color stable phosphor having thedesired properties. In some embodiments, the chamber containing thephosphor may be dosed and then sealed such that an overpressure developsas the chamber is heated, and in others, the fluorine and nitrogenmixture is flowed throughout the anneal process ensuring a more uniformpressure. In some embodiments, an additional dose of thefluorine-containing oxidizing agent may be introduced after a period oftime.

The annealed phosphor may be treated with a saturated or nearlysaturated solution of a composition of formula II in aqueoushydrofluoric acid

A_(x)[MF_(y)]   (II)

wherein

A is Li, Na, K, Rb, Cs, or a combination thereof,

M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Hf, Y, La, Nb, Ta, Bi, Gd, or acombination thereof,

x is an absolute value of a charge of the [MF_(y)] ion; and

y is 5, 6 or 7.

A nearly saturated solution contains about 1-5% excess aqueous HF addedto a saturated solution. The concentration of HF in the solution rangesfrom about 25% (wt/vol) to about 70% (wt/vol), in particular from about40% (wt/vol) to about 50% (wt/vol). Less concentrated solutions mayresult in reduced performance of the phosphor. The amount of treatmentsolution used ranges from about 2-30 ml/g product, particularly about5-20 ml/g product, more particularly about 5-15 ml/g product. Thetreated annealed phosphor may be isolated by filtration, washed withsolvents such as acetic acid and acetone to remove contaminants andtraces of water, and stored under nitrogen.

After treatment, the phosphor may optionally be contacted with afluorine-containing oxidizing agent in gaseous form at a second, lowertemperature. The second temperature may be the same as the firsttemperature, or may be less than the first, ranging up to and including225° C., particularly up to and including 100° C., and moreparticularly, up to and including 90° C. The time for contacting withthe oxidizing agent may be at least one hour, particularly at least fourhours, more particularly at least six hours, and most particularly atleast eight hours. In a specific embodiment, the phosphor is contactedwith the oxidizing agent for a period of at least eight hours at atemperature of about 90° C. The oxidizing agent may be the same as ordifferent from that used in the first annealing step. In particularembodiments, the fluorine-containing oxidizing agent is F₂. Moreparticularly, the atmosphere may include at least 20% F₂. The phosphormay be contained in a vessel having a non-metallic surface in order toreduce contamination of the phosphor with metals.

The Mn⁴⁺ doped phosphors of formula I may have a core-shell structurecomposed of a core which includes the phosphor of formula I and amanganese-free shell or composite coating disposed on the core. Themanganese-free composite coating includes a compound of formula III anda metal fluoride

A¹ _(x)[M¹F_(y)]   (III)

wherein A¹ is H, Li, Na, K, Rb, Cs, or a combination thereof,

M¹ is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or acombination thereof,

x is the absolute value of the charge of the [M¹F_(y)] ion; and

y is 5, 6 or 7.

The metal fluoride may be one or more of the following: calciumfluoride, strontium fluoride, magnesium fluoride, yttrium fluoride,scandium fluoride, and lanthanum fluoride. In particular embodiments,the phosphor of formula I is K₂[SiF₆]:Mn⁴⁺. The metal fluoride can be,in an embodiment, MgF₂. The core-shell Mn⁴⁺ doped phosphors of formula Iand methods for preparing them are described in WO 2018/093832. Asstated above, the Mn⁴⁺ doped phosphors of formula I may be combined with(or form part of a composition which is) a solution or suspension thatincludes one or more of the following substances: K₂HPO₄, an aluminumphosphate, oxalic acid, phosphoric acid, a surfactant, a chelatingagent, or a combination thereof. K₂HPO₄, an aluminum phosphate, oxalicacid, phosphoric acid, a surfactant, a chelating agent, or a combinationthereof shall be referred to herein as Substance. The weight ratio ofthe phosphor to the Substance may be from 200:1 to 1:1 and, morepreferably, is from 50:1 to 4:1. Examples of suitable chelating agentinclude, but are not limited to, ammonium citrate, potassium citrate,iminodiacetic acid (IDA), and ethylenediaminetetraacetic acid (EDTA).The surfactant may be nonionic, anionic, or cationic, or a mixturethereof. Examples of suitable surfactants include, but are not limitedto, aliphatic amines, fluorocarbon surfactants, stearic acid andstearate salts, and oleic acid and oleate salts. Suitable nonionicsurfactants include polyoxyethylene sorbitan fatty acid esters,commercially available under the TWEEN® brand, fluorocarbon surfactantssuch as NOVEC™ ammonium fluoroalkylsulfonamide, available from 3M, andpolyoxyethylene nonylphenol ethers. The surfactants (or other surfaceagents) can be one or more of polyoxyethylene octyl phenyl ether,potassium oleate, polyoxyethylene-polyoxypropylene block copolymer (suchas that sold as Pluronic F-127); polyoxyethylene (20) sorbitanmonolaurate (such as that sold as Tween 20), poly(acrylic acid sodiumsalt), potassium sorbate, sorbitan monooleate (such as that sold as Span80), and sodium hexametaphosphate. Additional examples of suitablesurfactants are described in US 2015/0329770, U.S. Pat. No. 7,985,723and Kikuyama, et al., IEEE Transactions on Semiconductor Manufacturing,vol. 3, No. 3, August 1990, pp. 99-108. In particular, the substance mayinclude K₂HPO₄. As stated above, the substance can also include asurfactant. The substance can include both the surfactant and K₂HPO₄.

The solution that the surfactant forms part of may include one or moreof the following solvents: 1-octadecene, isonorbornyl acrylate, water,and propylene glycol monomethyl ether acetate. It is noted that theorganic solutions of the present invention may include a minor amount ofwater. For example, there may be water present in the propylene glycolmonomethyl ether acetate (less than 0.05% by Karl Fischer), and also aminor amount of water in the potassium oleate. If the surfactant is partof an aqueous solution, such aqueous solution can also include H₂O₂. IfH₂O₂ is used, this can be in a range by weight of phosphor to H₂O₂ of200:1 to 1:1 and, more preferably, from 50:1 to 3:1.

An LED package or light emitting assembly or lamp 10 that may be used aspart of a display or lighting device or apparatus is shown in FIG. 1.LED package 10 includes a semiconductor radiation source, shown as LEDchip 12, and leads 14 electrically attached to the LED chip. The leads14 may be thin wires supported by a thicker lead frame(s) 16 or theleads may be self-supported electrodes and the lead frame may beomitted. The leads 14 provide current to LED chip 12 and thus cause itto emit radiation.

The lamp may include any semiconductor blue or UV light source that iscapable of producing white light when its emitted radiation is directedonto the phosphor. In one embodiment, the semiconductor light source isa blue emitting LED doped with various impurities. Thus, the LED maycomprise a semiconductor diode based on any suitable III-V, II-VI orIV-IV semiconductor layers and have an emission wavelength of about 250to 550 nm. In particular, the LED may contain at least one semiconductorlayer comprising GaN, ZnSe or SiC. For example, the LED may comprise anitride compound semiconductor represented by the formulaIn_(i)Ga_(j)Al_(k)N (where 0≤i; 0≤j; 0≤k, and i+j+k=1) and have anemission wavelength greater than about 250 nm and less than about 550nm. In particular embodiments, the chip is a near-uv or blue emittingLED having a peak emission wavelength from about 400 to about 500 nm.Such LED semiconductors are known in the art. The radiation source isdescribed herein as an LED for convenience. However, as used herein, theterm is meant to encompass all semiconductor radiation sourcesincluding, e.g., semiconductor laser diodes. Further, although thegeneral discussion of the exemplary structures of the inventiondiscussed herein is directed toward inorganic LED based light sources,it should be understood that the LED chip may be replaced by anotherradiation source unless otherwise noted and that any reference tosemiconductor, semiconductor LED, or LED chip is merely representativeof any appropriate radiation source, including, but not limited to,organic light emitting diodes.

In LED package 10, phosphor composition 22 is radiationally coupled tothe LED chip 12. Radiationally coupled means that the elements areassociated with each other so radiation from one is transmitted to theother. Phosphor composition 22 is deposited on the LED 12 by anyappropriate method. For example, a suspension of the phosphor(s) can beformed and applied as a phosphor layer to the LED surface. In one suchmethod, a silicone slurry in which the phosphor particles are randomlysuspended is placed around the LED. This method is merely exemplary ofpossible positions of phosphor composition 22 and LED 12. Thus, phosphorcomposition 22 may be coated over or directly on the light emittingsurface of the LED chip 12 by coating and drying the phosphor suspensionover the LED chip 12. In the case of a silicone-based suspension, thesuspension is cured at an appropriate temperature. Both the shell 18 andthe encapsulant 20 should be transparent to allow white light 24 to betransmitted through those elements.

In other embodiments, phosphor composition 22 is interspersed within theencapsulant material 20, instead of being formed directly on the LEDchip 12. The phosphor (in the form of a powder) may be interspersedwithin a single region of the encapsulant material 20 or throughout theentire volume of the encapsulant material. Blue light emitted by the LEDchip 12 mixes with the light emitted by phosphor composition 22, and themixed light appears as white light. If the phosphor is to beinterspersed within the material of encapsulant 20, then a phosphorpowder may be added to a polymer or silicone precursor, loaded aroundthe LED chip 12, and then the polymer precursor may be cured to solidifythe polymer or silicone material. Other known phosphor interspersionmethods may also be used, such as transfer loading.

In yet another embodiment, phosphor composition 22 is coated onto asurface of the shell 18, instead of being formed over the LED chip 12.The phosphor composition is preferably coated on the inside surface ofthe shell 18, although the phosphor may be coated on the outside surfaceof the shell, if desired. Phosphor composition 22 may be coated on theentire surface of the shell or only a top portion of the surface of theshell. The UV/blue light emitted by the LED chip 12 mixes with the lightemitted by phosphor composition 22, and the mixed light appears as whitelight. Of course, the phosphor may be located in any two or all threelocations or in any other suitable location, such as separately from theshell or integrated into the LED.

FIG. 2 illustrates a second structure of the system according to thepresent invention. Corresponding numbers from FIGS. 1-4 (e.g. 12 inFIGS. 1 and 112 in FIG. 2) relate to corresponding structures in each ofthe figures, unless otherwise stated. The structure of the embodiment ofFIG. 2 is similar to that of FIG. 1, except that the phosphorcomposition 122 is interspersed within the encapsulant material 120,instead of being formed directly on the LED chip 112. The phosphor (inthe form of a powder) may be interspersed within a single region of theencapsulant material or throughout the entire volume of the encapsulantmaterial. Radiation (indicated by arrow 124) emitted by the LED chip 112mixes with the light emitted by the phosphor 122, and the mixed lightappears as white light 124. If the phosphor is to be interspersed withinthe encapsulant material 120, then a phosphor powder may be added to apolymer precursor and loaded around the LED chip 112. The polymer orsilicone precursor may then be cured to solidify the polymer orsilicone. Other known phosphor interspersion methods may also be used,such as transfer molding.

FIG. 3 illustrates a third possible structure of the system according tothe present invention. The structure of the embodiment shown in FIG. 3is similar to that of FIG. 1, except that the phosphor composition 222is coated onto a surface of the envelope 218, instead of being formedover the LED chip 212. The phosphor composition 222 is preferably coatedon the inside surface of the envelope 218, although the phosphor may becoated on the outside surface of the envelope, if desired. The phosphorcomposition 222 may be coated on the entire surface of the envelope, oronly a top portion of the surface of the envelope. The radiation 226emitted by the LED chip 212 mixes with the light emitted by the phosphorcomposition 222, and the mixed light appears as white light 224. Ofcourse, the structures of FIGS. 1-3 may be combined, and the phosphormay be located in any two or all three locations, or in any othersuitable location, such as separately from the envelope, or integratedinto the LED.

In any of the above structures, the lamp 10 may also include a pluralityof scattering particles (not shown), which are embedded in theencapsulant material. The scattering particles may comprise, forexample, silica, alumina, zirconia, titania, zinc oxide, or acombination thereof. The scattering particles effectively scatter thedirectional light emitted from the LED chip, preferably with anegligible amount of absorption.

As shown in a fourth structure in FIG. 4, the LED chip 412 may bemounted in a reflective cup 430. The cup 430 may be made from or coatedwith a dielectric material, such as silica, alumina, zirconia, titania,or other dielectric powders known in the art, or be coated by areflective metal, such as aluminum or silver. The remainder of thestructure of the embodiment of FIG. 4 is the same as those of any of theprevious figures, and can include two leads 416, a conducting wire 432,and an encapsulant material 420. The reflective cup 430 is supported bythe first lead 416 and the conducting wire 432 is used to electricallyconnect the LED chip 412 with the second lead 416.

Another structure is a surface mounted device (SMD) type light emittingdiode 550, e.g. as illustrated in FIG. 5. This SMD is a “side-emittingtype” and has a light-emitting window 552 on a protruding portion of alight guiding member 554 and is particularly useful for backlightapplications. An SMD package may comprise an LED chip as defined above,and a phosphor material that is excited by the light emitted from theLED chip.

When used with an LED emitting light from 350 to 550 nm and one or moreother appropriate phosphors, the resulting lighting system will producea light having a white color.

In another embodiment, FIG. 6 illustrates a backlight unit or module 600according to the present invention that includes light source 602, lightguide panel 604, remote phosphor part in the form of a sheet or film606, filter 660, and LCD panel 616. Backlight unit 600 may alsooptionally include a prism 612 and a brightness enhancing film 614. Thelight source 602 is a blue emitting LED. To produce even lighting, bluelight from the light source 602 first passes through light guide panel604 which diffuses the blue light. The LCD panel 616 also includes colorfilters arranged in subpixels, a front polarizer, a rear polarizer, andliquid crystal as well as electrodes. Generally, there is an air spacebetween the LCD panel 616 and the brightness enhancing film 614. Thebrightness enhancing film 614 is a reflective polarizer film whichincreases efficiency by repeatedly reflecting any unpolarized lightback, which would otherwise be absorbed by the LCD's rear polarizer. Thebrightness enhancing film 614 is placed behind the liquid crystaldisplay panel 616 without any other film in-between. The brightnessenhancing film 614 may be mounted with its transmission axissubstantially parallel to the transmission axis of the rear polarizer.The brightness enhancing film 614 helps recycle the white light 622 thatwould normally be absorbed by the rear polarizer (not shown) of theliquid crystal panel 616, and thus increases the brightness of theliquid crystal display panel 616.

Remote phosphor part 606 includes particles 608A of a complex fluoridephosphor of formula I and particles 608B of a second light-emittingmaterial dispersed in a polymer resin. It is “remote” in the sense thatthe primary light source and the phosphor material are separateelements, and the phosphor material is not integrated with the primarylight source as a single element. Primary light is emitted from theprimary light source and is travels through one or more external mediato radiationally couple the LED light source to the phosphor material.It will be appreciated by those skilled in the art that a backlight unitaccording to the present invention may vary in configuration. Forexample, a direct lit configuration may be used. The prism 612 may alsobe removed or substituted by other brightness enhancement component inan alternative embodiment. The brightness enhancing film 614 may beremoved if desired.

In another embodiment, FIG. 7 shows a backlight unit 700 that includesbackplane 702, light guide panel 704, LED light source 706, mountingbracket 708, and a remote phosphor package in the form of a strip 710,mounted in the backplane 702. The remote phosphor part 710 is mountedvia mounting bracket 708 between light guide panel 704 and LED lightsource 706, whereby light emitting from the backlight source 706 istransmitted through part 710 and then enters the light guide plate 704.The backlight unit may further include a bottom reflector plate arrangedbetween light guide panel 704 and the backplane 702 and an optical filmassembly arranged above the light guide plate 704.

The LED radiationally coupled with the stabilized Mn⁴⁺ doped phosphormay form part of a display device. The display device may include theMn⁴⁺ doped phosphor radiationally coupled to a light emitting diode,including a mini light emitting diode or a micro light emitting diodewhich emits light in the blue spectrum. A micro light emitting diode(also known as a micro LED, microLED, micro-LED, mLED, and pLED), is atechnology utilized in displays in which there may be at least one smallLED device for each pixel on a screen, or there may be at least morethan one small LED device per pixel, and those LED devices may becoupled to red and green phosphors, respectively. Such a display devicemay include a backlighting unit and a) the stabilized Mn⁴⁺ dopedphosphor being part of the back lighting unit of the display device andbeing in direct or indirect contact with the LED or micro LED, or b) thestabilized Mn⁴⁺ doped phosphor being part of the back lighting unit andbeing remotely coupled to the LED or micro LED, and optionally being inthe form of a film. The stabilized Mn⁴⁺ doped phosphor may be operablyconnected to the back lighting unit through at least one filter, and theback lighting unit contains the light emitting diode or the micro lightemitting diode. In the display device, the Mn⁴⁺ doped phosphor may beoperably connected to or part of a back lighting unit of the displaydevice in any way that is known in the art.

In some embodiments, the Mn⁴⁺ doped phosphors according to the presentinvention are used in direct emission display devices that includearrays of microLEDs having dimensions on the scale of 1 to 300 μm or,more specifically, 1 to 100 μm, and even the scale of 1 to 50 μm, 1 to20 μm, or 1 to 10 μm. Exemplary methods for fabricating direct emissiondisplay devices that include phosphor particles in a wavelengthconversion layer coupled to the microLEDs are described in U.S. Pat.Nos. 9,111,464, and 9,627,437, and both of these patents areincorporated by reference herein in their entireties. Devices thatinclude a backlight unit or direct emission display according to thepresent invention include, but are not limited to, TVs, computers,smartphones, tablet computers and other handheld devices that have adisplay including a semiconductor light source; and a Mn⁴⁺ dopedphosphor according to the present invention. In an embodiment, thephosphor particles of the present invention are a part of a device whichcomprises an LED, quantum dots, a mini LED, or a micro LED. A mini LEDis an LED of a size between 50 μm and 300 μm. The display deviceaccording to the present invention may be a television, a computermonitor, a cellular or conventional phone, a digital photo frame, atablet, an automotive display, an e-book reader, an electronicdictionary, a digital camera, an electronic keyboard, or a gamingdevice, or any other electronic device with a screen.

Devices according to the present invention may include one or more otherlight emitting materials in addition to a Mn⁴⁺ doped phosphor. When usedin a lighting device or apparatus in combination with a blue or near UVLED emitting radiation in the range of about 250 to 550 nm, theresultant light emitted by the assembly may be a white light. Otherphosphors or quantum dot (QD) materials, such as green, blue, yellow,red, orange, or other color phosphors or QD materials may be used in ablend to customize the color of the resulting light and produce specificspectral power distributions. In other embodiments, the materials may bephysically separated in a multilayered structure or may be present inone or more blends in a multilayered structure. In FIGS. 1-5, phosphorcomposition 22 may be a single layer blend or a multilayered structurecontaining one or more phosphors or QD materials in each layer. InmicroLED direct emission display devices, individual microLEDs may beseparately coupled to a Mn⁴⁺ doped phosphor and other phosphors orquantum dot (QD) materials to yield light having desired specifications.

Suitable phosphors for use in devices according to the presentinvention, along with a Mn⁴⁺ doped phosphor include, but are not limitedto:

((Sr_(1−z)(Ca, Ba, Mg, Zn)_(z))_(1−(x+w))(Li, Na, K,Rb)_(w)Ce_(x))₃(Al_(1−y)Si_(y))O_(4+y+3(x−w))F_(1−y−3(x−w)), 0<x≤0.10,0≤y≤0.5, 0≤z≤0.5, 0≤w≤x;(Ca, Ce)₃Sc₂Si₃O₁₂ (CaSiG);(Sr,Ca,Ba)₃Al_(1−x)Si_(x)O_(4+x)F_(1−x):Ce³⁺ (SASOF));(Ba,Sr,Ca)₅(PO₄)₃(Cl,F,Br,OH):Eu²⁺,Mn²⁺;(Ba,Sr,Ca)BPOs:Eu²⁺,Mn²⁺;(Sr,Ca)₁₀(PO₄)₆*nB₂O₃:Eu²⁺ (wherein 0<n≤1); Sr₂Si₃O₈*2SrCl₂:Eu²⁺;(Ca,Sr,Ba)₃MgSi₂O₈:Eu²⁺,Mn²⁺; BaAlsO₁₃:Eu²⁺;2SrO*0.84P₂O₅*0.16B₂O₃:Eu²⁺;(Ba,Sr,Ca)MgAl₁₀O₁₇:Eu²⁺,Mn²⁺; (Ba,Sr,Ca)Al₂O₄:Eu²⁺;(Y,Gd,Lu,Sc,La)BO₃:Ce³⁺,Tb³⁺;ZnS:Cu⁺,Cl⁻; ZnS:Cu⁺,Al₃₊; ZnS:Ag⁺,Cl⁻; ZnS:Ag⁺,Al³⁺;(Ba,Sr,Ca)₂Si_(1−n)O_(4−2n):Eu²⁺ (wherein 0≤n≤0.2);(Ba,Sr,Ca)₂(Mg,Zn)Si₂O₇:Eu²⁺;(Sr,Ca,BaxAl,Ga,In)₂S₄:Eu²⁺;(Y,Gd,Tb,La,Sm,Pr,Lu)₃(A,Ga)_(5−a)O_(12−3/2a):Ce³⁺ (wherein 0≤a≤0.5);(Ca,Sr)₈(Mg,Zn)(SiO₄)₄Cl₂:Eu²⁺,Mn²⁺; Na₂Gd₂B₂O₇:Ce³⁺,Tb³⁺;(Sr,Ca,Ba,Mg,Zn)₂P₂O₇:Eu²⁺,Mn²⁺;(Gd,Y,Lu,La)₂O₃:Eu³⁺,Bi³⁺; (Gd,Y,Lu,La)₂O₂S:Eu³⁺,Bi³⁺;(Gd,Y,Lu,La)VO₄:Eu³⁺,Bi³⁺;(Ca,Sr)S:Eu²⁺,Ce³⁺; SrY₂S₄:Eu²⁺; CaLa₂S₄:Ce³⁺;(Ba,Sr,Ca)MgP₂O₇:Eu²⁺,Mn²⁺;(Y,Lu)₂WO₆:Eu³⁺,Mo⁶⁺;(Ba,Sr,Ca)_(b)Si_(g)N_(m):Eu²⁺ (wherein 2b+4g=3m); Ca₃(SiO₄)Cl₂:Eu²⁺;(Lu,Sc,Y,Tb)_(2−u−v)Ce_(v)Ca_(1−u)Li_(w)Mg_(2−w)P_(w)(Si,Ge)_(3−w)O_(12−u/2)(where −0.5≤u≤1, 0<v≤0.1, and 0≤w≤0.2); (Y,Lu,Gd)_(2+m)(Y,Lu,Gd)Ca_(m)Si₄N_(6+m)C_(1−m):Ce³⁺, (wherein0≤m≤0.5);(Lu,Ca,Li,Mg,Y), α-SiAlON doped with Eu²⁺ and/or Ce³⁺;(Ca,Sr,Ba)SiO₂N₂:Eu²⁺,Ce³⁺;β-SiAlON Eu²⁺,Ba[Li₂(Al₂Si₂)N₆]:Eu²⁺, 3.5MgO*0.5MgF₂*GeO₂:Mn⁴⁺;(Ca, Sr)_(1−c−f)Ce_(c)Eu_(f)Al_(1+c)Si_(1−c)N₃, (where 0≤c≤0.2,0≤f≤0.2);Ca_(1−h−r)Ce_(h)Eu_(r)Al_(1−h)(Mg,Zn)_(h)SiN₃, (where 0≤h≤0.2, 0≤r≤0.2);Ca_(1−2s−t)Ce_(s)(Li,Na)_(s)Eu_(t)AlSiN₃, (where 0≤s≤0.2, 0≤t≤0.2,s+t>0); (Sr, Ca)AlSiN₃: Eu²⁺,Ce³⁺(CASN);(Ba, Sr)₂Si₅N₈:Eu²⁺; Sr[LiAl₃N₄]:Eu²⁺; and Sr[Mg₃SiN₄]:Eu²⁺.U⁶⁺-doped phosphors may also be used; exemplary compositions includeBa₆Al₅P₅O₂₆: U⁶⁺, Ba₂P₂O: U⁶⁺, BaZn₂(PO₄)₂: U⁶⁺, and BaBPO: U⁶⁺. OtherU⁶⁺-doped phosphors are disclosed in US 2019/0088827, U.S. Ser. No.15/915,341, filed on 8 Mar. 2018, and U.S. Ser. No. 16/124,520, filed on7 Sep. 2018, all assigned to General Electric Company.

Quantum dot (QD) materials for use in devices according to the presentinvention may be a group II-VI compound, a group III-V compound, a groupIV-IV compound, a group IV compound, a group I-III-VI₂ compound or acombination thereof. Examples of group II-VI compounds include CdSe,CdTe, CdS, ZnSe, ZnTe, ZnS, HgTe, HgS, HgSe, CdSeTe, CdSTe, ZnSeS,ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS,CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, CdZnSeS, CdZnSeTe, CdZnSTe,CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe, or combinationsthereof. Examples of group III-V compounds include GaN, GaP, GaAs, AlN,AlP, AlAs, InN, InP, InAs, GaNP, GaNAs, GaPAs, AINP, AINAs, AIPAs, InNP,InNAs, InPAs, GaAINP, GaAINAs, GaAIPAs, GaInNP, GaInNAs, GainPAs,InAlNP, InAlNAs, InAlPAs, and combinations thereof. Examples of group IVcompounds include Si, Ge, SiC, and SiGe. Examples of group I-III-VI₂chalcopyrite-type compounds include CuInS₂, CuInSe₂, CuGaS₂, CuGaSe₂,AgInS₂, AgInSe₂, AgGaS₂, AgGaSe₂ and combinations thereof.

The QD materials may be a core/shell QD, including a core, at least oneshell coated on the core, and an outer coating including one or moreligands, preferably organic polymeric ligands. Exemplary materials forpreparing core-shell QDs include, but are not limited to, Si, Ge, Sn,Se, Te, B, C (including diamond), P, Co, Au, BN, BP, BAs, AlN, AlP,AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, AlN, AlP, AlAs,AlSb, GaN, GaP, GaAs, GaSb, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdSeZn,CdTe, HgS, HgSe, HgTe, BeS, BeSe, BeTe, MgS, MgSe, MnS, MnSe, GeS, GeSe,GeTe, SnS, SnSe, SnTe, PbO, PbS, PbSe, PbTe, CuF, CuCi, CuBr, CuI,Si₃N₄, Ge₃N₄, Al₂O₃, (Al, Ga, In)₂(S, Se, Te)₃, A₁₂CO, and appropriatecombinations of two or more such materials. Exemplary core-shell QDsinclude, but are not limited to, CdSe/ZnS, CdSe/CdS, CdSe/CdS/ZnS,CdSeZn/CdS/ZnS, CdSeZn/ZnS, InP/ZnS, PbSe/PbS, PbSe/PbS, CdTe/CdS andCdTe/ZnS.

The QD materials typically include ligands conjugated to, coordinatedwith, associated with, or attached to their surface. In particular, theQDs may include a coating layer comprising ligands to protect the QDsfrom environmental conditions including elevated temperatures, highintensity light, external gasses, and moisture. Such coating layer canalso help to control aggregation, and allow for dispersion of the QDs inthe matrix material.

Phosphor composition for use in display or lighting devices may includeone or more phosphors that result in a green spectral power distributionunder ultraviolet, violet, or blue excitation. In the context of thepresent invention, this is referred to as a green phosphor or greenphosphor material. The green phosphor may be a single composition or ablend that emits light in a green to yellow-green to yellow range, suchas cerium-doped yttrium aluminum garnets, more particularly(Y,Gd,Lu,Tb)₃(Al,Ga)₅O₁₂:Ce³⁺ (YAG). In some embodiments, an LED package10 has a color temperature less than or equal to 4200° K, and the onlyred phosphor present in phosphor composition 22 is the Mn⁴⁺ dopedphosphor; in particular, K₂SiF₆:Mn⁴⁺. The composition may additionallyinclude a green phosphor. The green phosphor may be a Ce³⁺-doped garnetor blend of garnets, particularly a Ce³⁺-doped yttrium aluminum garnet,and more particularly, YAG. When the red phosphor is K₂SiF₆:Mn⁴⁺, themass ratio of the red phosphor to the green phosphor material may beless than 3.3, which may be significantly lower than for red phosphorsof similar composition, but having lower levels of the Mn dopant. Othergreen-emitting that may be used with the Mn⁴⁺ doped phosphors includegreen-emitting QD materials and β-SiAlON.

The ratio of each of the individual phosphors in a phosphor blend mayvary depending on the characteristics of the desired light output. Therelative proportions of the individual phosphors in the variousembodiment phosphor blends may be adjusted such that when theiremissions are blended and employed in an LED lighting device, there isproduced visible light of predetermined x and y values on the CIEchromaticity diagram, and a white light is preferably produced. Thiswhite light may, for instance, possess an x value in the range of about0.20 to about 0.55, and a y value in the range of about 0.20 to about0.55. However, the exact identity and amounts of each phosphor in thephosphor composition can be varied according to the needs of the enduser. For example, the material can be used for LEDs intended for liquidcrystal display (LCD) backlighting. In this application, the LED colorpoint would be appropriately tuned based upon the desired white, red,green, and blue colors after passing through an LCD/color filtercombination. The list of potential phosphors for blending given here isnot meant to be exhaustive and these Mn⁴⁺ doped phosphors can be blendedwith various phosphors with different emission to achieve desiredspectral power distributions.

Other materials suitable for use in devices according to the presentinvention include electroluminescent polymers such as polyfluorenes,preferably poly(9,9-dioctyl fluorene) and copolymers thereof, such aspoly(9,9′-dioctylfluorene-co-bis-N,N′-(4-butylphenyl)diphenylamine)(F8-TFB); poly(vinylcarbazole) and polyphenylenevinylene and theirderivatives. In addition, the light emitting layer may include a blue,yellow, orange, green or red phosphorescent dye or metal complex, or acombination thereof. Materials suitable for use as the phosphorescentdye include, but are not limited to, tris(1-phenylisoquinoline) iridium(III) (red dye), tris(2-phenylpyridine) iridium (green dye) and Iridium(III) bis(2-(4,6-difluorephenyl)pyridinato-N,C2) (blue dye).Commercially available fluorescent and phosphorescent metal complexesfrom ADS (American Dyes Source, Inc.) may also be used. ADS green dyesinclude ADS060GE, ADS061GE, ADS063GE, and ADS066GE, ADS078GE, andADS090GE. ADS blue dyes include ADS064BE, ADS065BE, and ADS070BE. ADSred dyes include ADS067RE, ADS068RE, ADS069RE, ADS075RE, ADS076RE,ADS067RE, and ADS077RE.

The Mn⁴⁺ doped phosphors of the present invention may be used inapplications other than those described above. For example, the materialmay be used as a phosphor in a fluorescent lamp, in a cathode ray tube,in a plasma display device or in an LCD, as explained above. Thematerial may also be used as a scintillator in an electromagneticcalorimeter, in a gamma ray camera, in a computed tomography scanner orin a laser. These uses are merely exemplary and not limiting.

The present invention is also directed to certain inventive phosphorcompositions. For example, the present invention may be directed to aphosphor composition comprising phosphor particles and comprising, onsurfaces of the phosphor particles, at least one surface compositionselected from the group consisting of: 1) a composition containing aphosphorus-containing moiety and a carbon-containing moiety; 2) acomposition containing a phosphorus-containing moiety and a metalfluoride; 3) a composition containing a phosphorus-containing moiety anda carbon-containing moiety and a metal fluoride; and 4) a compositioncomprising the phosphorus-containing moiety free of an alkyl phosphatecompound, wherein the phosphor particles comprise a Mn⁴⁺ doped phosphorof formula I which is A_(x) [MF_(y)]:Mn⁴⁺, where A is Li, Na, K, Rb, Cs,or a combination thereof, M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y,La, Nb, Ta, Bi, Gd, or a combination thereof; x is the absolute value ofthe charge of the [MF_(y)] ion; y is 5, 6 or 7.

The surface composition containing a phosphorus-containing moiety may beformed by exposing the phosphor particles to K₂HPO₄. The surfacecomposition containing a carbon-containing moiety may be formed byexposing the phosphor particles to one or more of polyoxyethylene octylphenyl ether, potassium oleate, polyoxyethylene-polyoxypropylene blockcopolymer, polyoxyethylene (20) sorbitan monolaurate, poly(acrylic acidsodium salt), and potassium sorbate. The surface composition containinga phosphorus-containing moiety free of an alkylphosphate may be formedby exposing the phosphor particles to K₂HPO₄.

In one such composition, in an embodiment, the metal fluoride comprisesmagnesium fluoride. In another embodiment, the compound containingphosphorus comprises a phosphate moiety; in the context of the presentinvention, ‘phosphate’ means an ion that contains PO₄, and includes thephosphate ion, PO₄₃ hydrogen phosphate ion, HPO₄₂, and dihydrogenphosphate ion, H₂PO₄ ⁻. In yet another embodiment, the compoundcontaining carbon comprises at least one selected from the groupconsisting of: ethylenediaminetetraacetic acid, polyoxyethylene octylphenyl ether, potassium oleate, polyoxyethylene-polyoxypropylene blockcopolymer, polyoxyethylene (20) sorbitan monolaurate, poly(acrylic acidsodium salt), potassium sorbate, and derivatives or salts thereof.

The surface composition improves the quantum efficiency of the phosphorparticles upon exposure to liquid water or water vapor. In anembodiment, the phosphor particles exhibit A) a quantum efficiency afterexposure to liquid water for one hour at room temperature that is 50% to100% of the quantum efficiency exhibited before water exposure or B) aquantum efficiency loss upon exposure to 85% relative humidity at 85 degC. for 100 hours that is less than 40%.

An advantage of the present invention is that the phosphor particles areless agglomerated than would otherwise be the case. In an embodiment, aD₅₀ particle size of the phosphor particles before sonication of asolution containing the particles is no greater than 30 μm and the D₅₀particle size of the phosphor particles after sonication is no greaterthan 20 μm. In other words, the phosphor particles are sufficiently notagglomerated that the use of sonication will result in less of adecrease in agglomeration than would occur with particles which are nottreated pursuant to the present invention. Phosphor powders containingsubstantially unagglomerated particles may show improved flowability anddispersibility during LED package fabrication.

A light emitting diode device is a structure which contains a lightemitting diode. In an embodiment, a light emitting diode device isradiationally coupled to and/or comprises the phosphor compositionaccording to the present invention. In another embodiment, the lightemitting diode device is a mini LED or a micro LED. In yet anotherembodiment, a light emitting diode device can comprise an LED chip onwhich the phosphor composition is deposited. The phosphor composition isoptionally dispersed in a polymeric resin in a form of a film.

EXAMPLES

In the Examples mentioned below, the primary particle size was measuredusing a scanning electron microscope with procedures that are known inthe art, and the secondary particle size was measured using a HoribaLA-950V2 Laser Scattering Particle Size Distribution Analyzer, also withprocedures which are known in the art. Primary particle size accordingto the present application is the particle size of each phosphorparticle, whether in agglomerated state or not. The secondary particlesize according to the present application is the particle size of eachdiscreet particle or unit of particles. For example, if two 10 μmphosphor particles are agglomerated with one another, the primaryparticle size would be 10 μm since that is the size of each of the basicphosphor particles. In this scenario, the secondary particle size wouldbe more than 10 μm. For example, it may be 20 μm due to theagglomeration.

Span is a measure of the width of the particle size distribution curvefor a particulate material or powder, and is defined according toequation (1):

$\begin{matrix}{{Span} = \frac{\left( {D_{90} - D_{10}} \right)}{D_{50}}} & (1)\end{matrix}$

wherein

-   -   D₅₀ is the median particle size for a volume distribution;    -   D₉₀ is the particle size for a volume distribution that is        greater than the particle size of 90% of the particles of the        distribution; and    -   D₁₀ is the particle size for a volume distribution that is        greater than the particle size of 10% of the particles of the        distribution.

Quantum efficiency (QE) measurement is known in the art and can be done,for example, with a spectrometer. QE is a measure of blue photonsabsorbed/red photons emitted from luminescence of the phosphor. If thereis 100% QE, this means that every blue photon which is absorbed resultsin the emission of a red photon. QE is measured relative to a referencesample so in the present application, when QE's are compared, those arethe QEs relative to a reference sample. It is not critical whichreference sample is utilized since the comparison is of two or moreother samples relative to the reference sample so that the other two ormore samples can be compared to one another.

Determination of Robustness Against Contact with Water

Example 1

This example is directed to a phosphor having chemical formulaK₂SiF₆:Mn⁴⁺. This phosphor powder had an average primary particle sizeof 10.5 μm as determined by scanning electron microscopy. This phosphorwas not stabilized as described in the present application nor exposedto a water test.

Example 2

1 g of the phosphor of Example 1 was mixed with 3 g deionized water in a15 mL plastic bottle. The mixture was shaken by hand for 15 seconds andthen rolled at 40 rpm for 1 hour. The mixture was filtered on Whatman #4filter paper and washed 4 times with a total of 100 mL acetone (i.e.,100 mL of acetone was used to effectuate the 4 washes). The powder wasdried under vacuum for at least 24 hours.

Example 3

1.2 g of the phosphor of Example 1 was mixed with 3.6 g of a 39 mMsolution of phosphoric acid in a 15 mL plastic bottle. The mixture wasshaken by hand for 15 seconds and then rolled at 40 rpm for 1 hour. Themixture was filtered on Whatman #4 filter paper and washed 4 times witha total of 100 mL acetone. The powder was dried under vacuum for atleast 18 hours. The powder was added to a fresh bottle and mixed withdeionized water in a 1 g:3 g ratio of powder to water. The mixture wasshaken by hand for 15 seconds and then rolled at 40 rpm for 1 hour. Themixture was filtered on Whatman #4 filter paper and washed 4 times witha total of 100 mL acetone. The powder was dried under vacuum for atleast 24 hours.

Example 4

The experiment of Example 3 was repeated, replacing 39 mM phosphoricacid with 390 mM phosphoric acid.

Example 5

The experiment of Example 3 was repeated, replacing 39 mM phosphoricacid with 39 mM oxalic acid.

Example 6

The experiment of Example 3 was repeated, replacing 39 mM phosphoricacid with 390 mM oxalic acid.

Example 7

The experiment of Example 3 was repeated, replacing 39 mM phosphoricacid with 39 mM potassium hydrogen phosphate, dibasic.

Example 8

The experiment of Example 3 was repeated, replacing 39 mM phosphoricacid with 390 mM potassium hydrogen phosphate, dibasic (pH 9).

Cured films of a 2-part thermally cured polydimethylsiloxane elastomer(such as is sold as Sylgard 184, from Dow Corning) comprising dispersedphosphor particles were prepared at a concentration of 0.5 g of phosphorper 1.5 g of silicone. The phosphors used were the ones prepared inExamples 1-8. The quantum efficiencies (QE) of the phosphor particleswere measured in these films.

The results of QE measurements on phosphor containing films aresummarized in Table 1 for Examples 1-8.

TABLE 1 Measured QE values for the phosphor containing films of Examples1-8. Example Details QE 1 Starting material K₂SiF₆:Mn⁴⁺ 105.6% 2Control - starting K₂SiF₆:Mn⁴⁺ (from 74.6% Example 1 mixed with water 3K₂SiF₆:Mn⁴⁺ from 86.2% Example 1 mixed with 39 mM H₃PO₄ then water 4K₂SiF₆:Mn⁴⁺ from 90.3% Example 1 mixed with 390 mM H₃PO₄ then water 5K₂SiF₆:Mn⁴⁺ from 80.1% Example 1 mixed with 39 mM oxalic acid then water6 K₂SiF₆:Mn⁴⁺ from 85.3% Example 1 mixed with 390 mM oxalic acid thenwater 7 K₂SiF₆:Mn⁴⁺ 100.7% from Example 1 mixed with 39 mM K₂HPO₄ thenwater 8 K₂SiF₆:Mn⁴⁺ from 104.2% Example 1 mixed with 390 mM K₂HPO₄ thenwater

The data in Table 1 shows that the robustness of K₂SiF₆:Mn⁴⁺ phosphor isenhanced by a process comprising mixing K₂SiF₆:Mn⁴⁺ with an aqueoussolution of several substances, such as K₂HPO₄, followed by powderisolation and drying. Enhanced robustness is shown as a preservation ofQE after mixing the treated phosphor powder with water for 1 hour, vsthe QE of the untreated powder as produced mixed with water for 1 hour,relative to the QE of the starting phosphor powder without mixing withwater. The QE of Example 1 is 105.6%, which is not treated with water.The QE of Example 2 is 74.6%, which shows that water can have a largedetrimental effect on the QE of phosphors. Example 2 is not treated inaccordance with the present invention. Example 3 is treated inaccordance with the present invention and exhibits a QE of 86.2%, whichis much higher than a QE of 74.6%. In the technology for phosphors, evena small percentage change in QE is significant and phosphormanufacturers are routinely looking for ways to add even a fewpercentage points of QE to their phosphors. Thus, a jump from 74.6% to86.2% is significant and surprising. Of the Examples above, the effectof treating the phosphor powder with an aqueous solution of K₂HPO₄ wasmost pronounced in maintaining QE, since Examples 7 and 8 show a QE of100.7% and 104.2%, respectively.

Example 9

This Example is directed to a phosphor having chemical formulaK₂SiF₆:Mn⁴⁺. This phosphor was not stabilized as described in thepresent application nor exposed to a water test. The K₂SiF₆:Mn⁴⁺phosphor of Example 9 had an average primary particle size of 10.0 μm asdetermined by scanning electron microscopy. Furthermore, the phosphor ofExample 9 was not treated with an HF solution of K₂SiF₆ after annealing.

Example 10

The phosphor used in Example 10 is the same as in Example 1, and bothare treated with an HF solution saturated with K₂SiF₆ after annealing.The Examples are duplicates of one another. The fact that they getsimilar results for QE means that this experiment is repeatable.

Example 11

A K₂SiF₆:Mn⁴⁺ phosphor was utilized which has a smaller average primaryparticle size as Examples 1 and 9. The phosphor powder of Example 11 hadan average primary particle size of 3.9 μm as determined by scanningelectron microscopy and did not receive stabilizing treatment accordingto the present invention.

Example 12

A K₂SiF₆:Mn⁴⁺ phosphor was utilized which has a smaller average particlesize than Examples 1 and 9. The phosphor of Example 12 had an averageprimary particle size of 3.9 μm as determined by scanning electronmicroscopy and did not receive stabilizing treatment according to thepresent invention.

Examples 13-16

In four separate experiments, 1 g of each of the phosphor samples fromExample 9, Example 1, Example 11, and Example 12, respectively, wasmixed with 3 g deionized water in a 15 mL plastic bottle. The mixtureswere shaken by hand for 15 seconds and then rolled at 40 rpm for 1 hour.The mixtures were filtered on Whatman #4 filter paper and each washed 4times with a total of 100 mL acetone. The powders were dried undervacuum for at least 24 hours.

Examples 17-20

In four separate experiments, 1.2 g of each of the phosphor samples fromExample 9, Example 1, Example 11, and Example 12, respectively, wasmixed with 3.6 g of a 390 mM solution of potassium hydrogen phosphate,dibasic (pH 9), in a 15 mL plastic bottle. The mixtures were shaken byhand for 15 seconds and then rolled at 40 rpm for 1 hour. The mixtureswere filtered on Whatman #4 filter paper and each washed 4 times with atotal of 100 mL acetone. The powders were dried under vacuum for atleast 18 hours. The powders were then added to a fresh bottle and mixedwith deionized water in a 1 g:3 g ratio of powder to deionized water.The mixtures were shaken by hand for 15 seconds and then rolled at 40rpm for 1 hour. The mixtures were filtered on Whatman #4 filter paperand each washed 4 times with a total of 100 mL acetone. The powders weredried under vacuum for at least 24 hours.

Example 21

1.2 g of the phosphor sample of Example 1 was mixed with 3.6 g of a 390mM solution of potassium hydrogen phosphate, dibasic (pH 9), in a 15 mLplastic bottle. The mixture was shaken by hand for 15 seconds and thenrolled at 40 rpm for 15 minutes. The mixture was filtered on Whatman #4filter paper and then washed 4 times with a total of 100 mL acetone. Thepowder was dried under vacuum for 4 hours. The powder was then added toa fresh bottle and mixed with deionized water in a 1 g:3 g ratio ofpowder to deionized water. The mixture was shaken by hand for 15 secondsand then rolled at 40 rpm for 1 hour. The mixture was filtered onWhatman #4 filter paper and then washed 4 times with a total of 100 mLacetone. The powder was dried under vacuum for at least 24 hours.

Example 22

The experiment of Example 21 was repeated except that the aqueous 390 mMK₂HPO₄ solution mixed with the phosphor of Example 1 was rolled for 90minutes instead of 15 minutes.

Example 23

1.2 g of phosphor from Example 1 was mixed with 3.6 g of a 390 mMsolution of potassium hydroxide (pH 13.5) in a 15 mL plastic bottle. Themixture was shaken by hand for 15 seconds and then rolled at 40 rpm for1 hour. The mixture was filtered on Whatman #4 filter paper and thenwashed 4 times with a total of 100 mL acetone. The powder was driedunder vacuum for 4 hours. The powder was then added to a fresh bottleand mixed with deionized water in a 1 g:3 g ratio of powder to ionizedwater. The mixture was shaken by hand for 15 seconds and then rolled at40 rpm for 1 hour. The mixture was filtered on Whatman #4 filter paperand then washed 4 times with a total of 100 mL acetone. The powder wasdried under vacuum for at least 24 hours.

Example 24

The experiment of Example 23 was repeated except that the 390 mMsolution of KOH was replaced with a more dilute aqueous KOH solutionadjusted to pH 9.

TABLE 2 Measured QE values for the phosphor containing films of Examples9-24. Description Ex Details QE Starting 9 Starting material K₂SiF₆:Mn⁴⁺104.9% material of Example 9 (SM) 10 Starting material K₂SiF₆:Mn⁴⁺104.8% of Example 1 11 Starting material K₂SiF₆:Mn⁴⁺ 97.6% of Example 1112 Starting material K₂SiF₆:Mn⁴⁺ 98.5% of Example 12 Control 13K₂SiF₆:Mn⁴⁺ 62.7% samples: of Example 9 mixed with water SM's 14K₂SiF₆:Mn⁴⁺ 73.7% mixed of Example 1 mixed with water with 15K₂SiF₆:Mn⁴⁺ 25.0% water of Example 11 mixed with water 16 K₂SiF₆:Mn⁴⁺25.1% of Example 12 mixed with water Effect of 17 K₂SiF₆:Mn⁴⁺ 104.3%mixing SM of Example 9 mixed with 390 mM with aq K₂HPO₄ 1 h, then waterK₂HPO₄ 18 K₂SiF₆:Mn⁴⁺ 104.5% before of Example 1 mixed with 390 mMmixing K₂HPO₄ 1 h, then water with 19 K₂SiF₆:Mn⁴⁺ 91.9% water of Example11 mixed with 390 mM K₂HPO₄ 1 h, then water 20 K₂SiF₆:Mn⁴⁺ 93.5% ofExample 12 mixed with 390 mM K₂HPO₄ 1 h, then water Effect of 21K₂SiF₆:Mn⁴⁺ 104.4% aq K₂HPO₄ of Example 1 mixed with 390 mM mixingK₂HPO₄ 15 min, then water time 22 K₂SiF₆:Mn⁴⁺ 104.9% of Example 1 mixedwith 390 mM K₂HPO₄ 1.5 h, then water Effect of 23 K₂SiF₆:Mn⁴⁺ 75.6%mixing with of Example 1 mixed with 390 mM aq KOH KOH 1 h, then water 24K₂SiF₆:Mn⁴⁺ 51.0% of Example 1 mixed with pH 9 KOH 1 h, then water

The data shown in Table 2 confirms that mixing K₂SiF₆:Mn⁴⁺ phosphorpowder with water has a significant detrimental effect on the phosphor'sQE. Examples 17 and 18 clearly show that when the phosphor powder ismixed with an aqueous solution of K₂HPO₄ prior to mixing with purewater, the phosphor powder is rendered surprisingly more robust againstdegradation upon subsequent exposure to water. Degradation is indicatedby a drop in QE, and samples 13-16, without K₂HPO₄ exposure, showed muchlower QE than Examples 17-20 which were treated with K₂HPO₄. Moreover,without intending to be bound by any theory, this measure of stabilityor robustness is durable in the sense that the benefit persists evenafter isolation of the powder from the aqueous K₂HPO₄ treatmentsolution, washing and drying. The data shows that the stabilization ofthe powder is surprisingly fast since the QE of powder mixed withaqueous K₂HPO₄ for just 15 minutes was essentially the same as when themixing time was 1 hour or even 90 minutes. In Examples 18, 21 and 22, 15minutes of exposure to aqueous K₂HPO₄ resulted in a QE that was just ashigh as the QE after 90 minutes exposure. The phosphor powder issubstantially stable in the K₂HPO₄ treatment solution over extended timeperiods in spite of the fact that the aqueous K₂HPO₄ is mostly waterwhich is known to degrade phosphors.

Examples 11, 12, 15 and 16 are untreated with K₂HPO₄ and include samplesof small particle sizes. Examples 19 and 20 are both treated with K₂HPO₄and include samples with small particle sizes. The results for Examples19 and 20 show that the stabilization resulting from treatment of thephosphor powder with aqueous K₂HPO₄ is surprisingly high even when theK₂SiF₆:Mn⁴⁺ powder has a primary particle size of 3.9 μm.

The surprising stabilization afforded upon treatment of the phosphorwith aqueous K₂HPO₄ is not just a pH effect. As shown in Example 24,mixing phosphor powder with an aqueous solution of KOH that waspH-adjusted to match the pH of 390 mM K₂HPO₄ (see Examples 17-20) didnot result in phosphor stabilization. In fact, the QE of Example 24 wasjust 51%, which is even lower than Example 14 (which was acidic with apH of 3.28) which had a QE of 73.7% and which was not mixed with astabilization agent. In other words, adjusting the pH with KOH to bebasic (Example 24) resulted in a much worse result than adding nostabilization agent (Example 14). A significant QE drop was alsoobserved in Example 23 (QE of 75.6%) when the phosphor powder was mixedwith aqueous KOH (pH 13.48) that matched the concentration of the K₂HPO₄solutions (390 mM) in Examples 17-22 where the lowest QE was 91.9%.

Reduction of Agglomeration

In order to reduce the agglomeration of phosphor particles, severaltreatments were tested. The objective is to reduce agglomeration so thatdispersibility in resins is improved, such that if the phosphor powdersare dispersed in, say, films of photoresist or hydrophobic acrylates,the phosphors are uniformly distributed. Various combinations ofsolvents and surfactants were used. Typical solvents ranged fromnon-polar hydrocarbon solvents such as 1-octadecene (ODE) to moderatelypolar isonorbornyl acrylate to polar aprotic propylene glycol monomethylether acetate (PGMEA). Surfactant/dispersant additives included thosethat are non-ionic (oleylamine, oleic acid, polyoxyethylene octyl phenylether (which may be sold as Triton X-100)), anionic (potassium oleate)and cationic (polyethylene oxide derivatized fatty ammonium ethosulphate(which may be marketed as Hypermer KD25-LQ-(MV)). Examples 25-71 hadsecondary particle size d50 measured using light scattering.

Example 25

Example 25 is a control and consisted of 3 g of K₂SiF₆:Mn⁴⁺ powderhaving a secondary particle size d50 of 15.0 μm. No solvent orsurfactant/dispersant was added. This control was used to determine thevalues of the second column of Table 3 (Δd50−ODE+roller (μm)).

Example 26

Example 26 had organic solvent and no surfactant, and was made by taking3 g of K₂SiF₆:Mn⁴⁺ powder from the same lot as Example 25 and mixing itwith 20 mL of ODE which is an organic solvent. Then, the resultingcomposition was shaken briefly to mix and rolled at 80 rpm for 20-30minutes. The resulting mixture was then vacuum filtered to collect thepowder and rinsed with 3×20 mL of acetone to remove traces of solvent.Following the acetone wash the powder was dried on the filter for nomore than five minutes before being collected and dried in a vacuumdesiccator for at least 4 hours. The dry powders were then sievedthrough a 170 mesh screen to improve flowability and then stored in anitrogen purged box/cabinet until they could be analyzed for particlesize distribution (PSD) and quantum efficiency (QE). The secondaryparticle size d50 was then compared with that measured for Example 25and the difference or “delta” was recorded in the second column of Table3. The Δd50 was −1.4 μm, so the d50 of Example 26 was 1.4 μm less thanthe d50 of Example 25. Thus, the use of ODE as solvent reduced thesecondary particle size of the sample.

Examples 27-31

Examples 27-31 were made by taking 20 mL of ODE and combining it with0.3 g of a respective surfactant as identified on the first column ofTable 3, and then adding 3 g of K₂SiF₆:Mn⁴⁺ powder from the same lot asExample 25. Then, the resulting composition was shaken briefly to mixand rolled at 80 rpm for 20-30 minutes. The resulting mixture was thenvacuum filtered to collect the powder and rinsed with 3×20 mL of acetoneto remove traces of solvent. Following the acetone wash the powder wasdried on the filter for no more than five minutes before being collectedand dried in a vacuum desiccator for at least 4 hours. The dry powderswere then sieved through a 170 mesh screen to improve flowability andthen stored in a nitrogen purged box/cabinet until they could beanalyzed for secondary particle size and QE. The secondary particle sized50s were then compared with Example 25 and the difference for each, or“delta” was recorded at the second column of Table 3.

Example 32

Example 32 is a control and consists of 3 g of K₂SiF₆:Mn⁴⁺ powder havinga secondary particle size d50 of 33.4 μm. No solvent orsurfactant/dispersant was added. The QE of Example 32 was 92.8%. Thiscontrol was used to determine the values of the third column of Table 3(Δd50−PGMEA+roller (μm)).

Example 33

Example 33 has organic solvent and no surfactant, and was made by taking3 g of K₂SiF₆:Mn⁴⁺ powder from the same lot as Example 32 and mixing itwith 20 mL of propylene glycol monomethyl ether acetate (PGMEA) which isan organic solvent. Then, the resulting composition was shaken brieflyto mix and rolled at 80 rpm for 20-30 minutes. The resulting mixture wasthen vacuum filtered to collect the powder and rinsed with 3×20 mL ofacetone to remove traces of solvent. Following the acetone wash thepowder was dried on the filter for no more than five minutes beforebeing collected and dried in a vacuum desiccator for at least 4 hours.The dry powder was then sieved through a 170 mesh screen to improveflowability and then stored in a nitrogen purged box/cabinet until itcould be analyzed for PSD and QE. The secondary particle sizedistribution d50 was then compared with Example 32 and the difference or“delta” was recorded in Table 3, so Δd50 was −18.6 μm so the d50 ofExample 33 was 18.6 μm less than the d50 of Example 32.

Examples 34-38

Examples 34-38 were made by taking 20 mL of PGMEA and combining it with0.3 g of a particular surfactant as identified at column 1 of Table 3and then adding 3 g of K₂SiF₆:Mn⁴⁺ powder from the same lot as Example32. Then, the resulting composition was shaken briefly to mix and rolledat 80 rpm for 20-30 minutes. The resulting mixture was then vacuumfiltered to collect the powder and rinsed with 3×20 mL of acetone toremove traces of solvent. Following the acetone wash the powder wasdried on the filter for no more than five minutes before being collectedand dried in a vacuum desiccator for at least 4 hours. The dry powderswere then sieved through a 170 mesh screen to improve flowability andthen stored in a nitrogen purged box/cabinet until they could beanalyzed for PSD and QE. The particle size d50 was then compared withExample 32 and the differences or “deltas” was recorded in Table 3 atcolumn 3.

Example 39

Example 39 is a control and consists of 3 g of K₂SiF₆:Mn⁴⁺ powder havinga secondary particle size d50 of 35.2 μm. No solvent orsurfactant/dispersant was added. The QE for this sample was determinedto be 94.1%. Example 39 is the control used in conjunction with columns4-6 of Table 3 (Δd50−PGMEA+ultrasound (μm); Δd50−acrylate+roller (μm);Δd50−acrylate+ultrasound (μm), respectively).

Example 40

Example 40 had organic solvent and no surfactant, and was made by taking3 g of K₂SiF₆:Mn⁴⁺ powder from the same lot as Example 39 and mixing itwith 20 mL of isonorbornyl acrylate which is an organic solvent. Then,the resulting composition was shaken briefly to mix and rolled at 80 rpmfor 20-30 minutes. The resulting mixture was then vacuum filtered tocollect the powder and rinsed with 3×20 mL of acetone to remove tracesof solvent. Following the acetone wash the powder was dried on thefilter for no more than five minutes before being collected and dried ina vacuum desiccator for at least 4 hours. The dry powders were thensieved through a 170 mesh screen to improve flowability and then storedin a nitrogen purged box/cabinet until they could be analyzed forsecondary PSD and QE. The secondary particle size d50 was then comparedwith Example 39 and the difference or “delta” was recorded at column 5of Table 3, so Δd50 was −19.4 μm so the d50 of Example 40 was 19.4 umless than the d50 of Example 39.

Examples 41-47

Examples 41-47 were made by taking 20 mL of PGMEA (for Examples 41-43)or 20 mL of isonorbornyl acrylate (Examples 44-47) and combining eachwith 0.3 g of a surfactant identified at the last three lines of column1 of Table 3. Subsequently, 3 g of K₂SiF₆:Mn⁴⁺ powder from the same lotas Example 39 was added. Then, the resulting composition was shakenbriefly to mix and subjected to either an ultrasonic bath treatment for7 minutes (Examples 41-43 and 47) or rolled at 80 rpm for 20-30 minutes(Examples 44-46). The resulting mixtures were then vacuum filtered tocollect the powder and rinsed with 3×20 mL of acetone to remove tracesof solvent. Following the acetone wash the powder was dried on thefilter for no more than five minutes before being collected and dried ina vacuum desiccator for at least 4 hours. The dry powders were thensieved through a 170 mesh screen to improve flowability and then storedin a nitrogen purged box/cabinet until they could be analyzed forsecondary PSD and QE. The secondary particle size d50 was then comparedwith Example 39 and the difference or “delta” was recorded in Table 3.Examples 41-43 are recorded at column 4 (Δd50−PGMEA+ultrasound (μm)),Examples 44-46 are recorded at column 5 (Δd50−acrylate+roller (μm)), andExample 47 is recorded at column 6 (Δd50−acrylate+ultrasound (μm)) ofTable 3. The absolute secondary particle size d50 (i.e., not relative toExample 39) of sample 41 is 12.9 μm and the QE was 88.4%. The absolutesecondary particle size d50 (i.e., not relative to Example 39) of sample42 was 12.0 μm and the QE is 94.3%. The absolute secondary particle sized50 (i.e., not relative to Example 39) d50 of sample 43 was 12.5 μm andthe QE was 94.2%.

TABLE 3 Particle size distribution reduction without sonication duringmeasurement upon surf actant/dispersant treatment of K₂SiF₆:Mn⁴⁺powders. Δd50 − Δd50 − Δd50 − Δd50 − Δd50 − ODE + PGMEA + PGMEA +acrylate + acrylate + roller roller ultrasound roller ultrasoundSurfactant (μm) (μm) (μm) (μm) (μm) None −1.4 −18.6 −19.4 Oleic acid+9.7 −13.9 (asym) Oleylamine +6.6 −18.5 (asym) Potassium −0.1 −20.3−22.3 −21.2 −22.7 oleate polyoxy- +4.4 −19.4 −23.2 −21.0 ethylene octylphenyl ether PODFAE −3.2 −18.9 −22.7 −19.2

As can be seen in Table 3, the use of certain solvents can help reduceagglomeration. The use of certain surfactants can also reduceagglomeration. Certain combinations of solvents and surfactants exhibitadvantages as well. Regardless of the extent of agglomeration in theinitial powder, the potassium oleate, polyoxyethylene octyl phenylether, and polyethylene oxide derivatized fatty ammonium ethosulphate(PODFAE) such as may be obtained as Hypermer KD25-LQ-(MV), as theleading anionic, non-ionic, and cationic additive candidates,respectively, resulted in a secondary particle size with absolutesecondary d50 of 12-14 μm (i.e., not relative to another sample). Thecomparison to the controls is shown in Table 3.

Variants of the examples shown above also demonstrate the advantages ofthe present invention. Examples 48-51 below exemplify this and theresults are in Table 4.

Example 48

This is a control which is K₂SiF₆:Mn⁴⁺ without any surface treatment. Inother words, no KEDTA nor K₂HPO₄, nor potassium oleate, nor PGMEA, norMgF₂ coated phosphor, nor MgSiF₆.6H₂O, nor H₂SiF₆.

Example 49

This sample is directed to treatment of K₂SiF₆:Mn⁴⁺ withethylenediaminetetraacetic acid dipotassium salt dihydrate (KEDTA). Asolution was prepared by adding 16.3 g K₂HPO₄, 6.4 g KEDTA, 22 mLaqueous 30% H₂O₂, and 480 mL distilled H₂O to a 1 L polypropylene bottlesuch that the pH was between 7-8. To that, 128 g K₂SiF₆:Mn⁴⁺ was addedand the bottle was rolled at 40 RPM for 20 minutes. The material wasthen allowed to settle, the supernatant decanted and the slurry wasvacuum filtered, rinsed once with 100 mL of H₂O+2 mL 30% H₂O₂, and then5 times with 100 mL of acetone before drying under vacuum.

It is also possible to optionally rinse the samples with acetic acid andethanol, and to dry the samples under vacuum at elevated temperature upto 200° C. It is also possible to optionally use ultrasonication inplace of/in combination with rolling the bottle.

Example 50

This sample is directed to K₂SiF₆:Mn⁴⁺ treatment with potassium oleatein organic media. Potassium oleate (7.5229 g, 23.47 mmol, 40 wt % pastein water from Sigma Aldrich, 5 wt % relative to K₂SiF₆:Mn⁴⁺) wasdissolved in 250 mL PGMEA. This solution was added to a 1 gallon plasticbottle containing 150.14 g K₂SiF₆:Mn⁴⁺ powder and 250 mL of PGMEA. Threeadditional 250 mL portions PGMEA were used to rinse the potassium oleatecontainer and added to the one gallon bottle containing theK₂SiF₆:Mn⁴⁺/surfactant mixture (total PGMEA=1.25 L). The one gallonbottle was capped and rolled for 30 minutes. The resulting stabilizedphosphor powder was transferred to a plastic Buchner funnel and isolatedby vacuum filtration. 500 mL of acetone was used to rinse the one gallonplastic bottle and was transferred to the Buchner funnel to wash thesolid. Three additional 500 mL portions of acetone were used to wash thesolid, churning the solid before each wash (total 2 L acetone), whichwas then air dried for 3 minutes. The slightly wet powder was collectedand dried for three days in a vacuum desiccator and then sifted througha 170 mesh membrane to afford 146.77 g of surfactant treated K₂SiF₆:Mn⁴⁺product.

Example 51

This sample is directed to MgF₂ coated phosphor. MgSiF₆.6H₂O (17.6992 g,64.48 mmol) was weighed into a 60 mL plastic jar to which was then added40 g of high purity deionized water. After mixing, the slightly cloudymixture was filtered through a 0.45 μm membrane. The filtered solutionwas diluted with 40 mL of 35% aq H₂SiF₆ (52.8 g, density 1.32). Thismade solution A. Separately, 125 g of K₂SiF₆:Mn⁴⁺ was added to a 2 L mLplastic beaker containing a large stir bar. Each of two syringe pumpswere set up to deliver 37.5 mL of solution A over 30 minutes (75 mL ofsolution A total) directly into the reaction mixture. To the beakercontaining the phosphor powder was added 1.425 L of aq 49% HF saturatedwith K₂SiF₆. The mixture was stirred vigorously for 30 sec (300 rpm)after which the stirring was turned down to 120 rpm. The addition of thesolution A into the stirring reaction mixture via syringe pump wasinitiated. After the addition was complete, the stirring was stopped,the stir bar was removed and the reaction mixture was allowed to settlefor 10 minutes. The supernatant was decanted and discarded. The wetslurry was mixed with 400 mL of 49% aq HF saturated with K₂SiF₆ andMgF₂. The wash mixture was allowed to settle for 10 minutes and then thesupernatant was decanted and discarded. The slurry was transferred to aplastic Buchner funnel fitted with a 0.65 μm fluoropolymer membrane. Theresidual HF solution was filtered off and the phosphor cake was washedwith acetone 4 times, using a total of 800 mL acetone, churning thesolid before each wash. The product was dried under vacuum for 3 daysand then sifted through a 170 mesh membrane to afford the final product.The results of the testing of Examples 48-51 are shown at Table 4.

TABLE 4 D50 D50 US Example (μm) (μm) Rel QE, % 48 (Control) 26 14 105 4920 11 106 50 14 11 105 51 19 14 104

The D50 secondary particle size of samples 48-51 were measured asfollows:

-   -   1. D50 measurements in Table 4. Completed on an Horiba 950 with        no sonication but circulation set to 5 for 3 minutes prior to        measurement. Solvent is isopropyl alcohol.    -   2. D50 US measurements in Table 4. Completed like measurement        above but with a ultrasonication set to 7 in addition to the        circulation set to 5.

The Horiba measurement gives an agglomerated size, which is the size ofthe agglomerated masses of basic particles. The US measurement gives aminimally agglomerated size, which means that it is the agglomeratedmasses of basic particles decreased somewhat by the ultrasonication.

The examples 48-51 show that the surface treatments and MgF₂ coatingsurprisingly produce a less agglomerated particle size with little to nodrop in quantum efficiency.

Examples 52-76 also show the concomitant maintenance of a good quantumefficiency with a reduction of agglomeration of particles, as explainedbelow.

Example 52

This is a batch of K₂SiF₆:Mn⁴⁺ which was used in all of Examples 53-76.

Example 53

This is the control batch. 4 g K₂SiF₆:Mn⁴⁺ from Example 52 was put in 20mL H₂O in a 30 mL Nalgene bottle. It was rolled for 30 minutes at 80RPM. The sample was then settled for 20 minutes, subjected to acentrifuge pulse to 2500 RPM (˜30 sec), then decanted, vacuum filtered,washed with acetone 3 times, vacuum dried, and sifted through a 170 meshmembrane. Example 53 does not contain the surface agents of the presentinvention and is being compared to samples with surface agents.

Examples 54-76

Examples 54-76 were made as follows: 4 g K₂SiF₆:Mn⁴⁺ from Example 52 wasput in 20 mL H₂O or 20 mL 0.78M K₂HPO₄ (aq)+0.3 g or 0.6 g (or 0.3 mL)of surface agent in a 30 mL Nalgene bottle. The bottle was rolled for 30minutes at 80 RPM. The sample was then settled for 20 minutes, subjectedto a centrifuge pulse to 2500 RPM (˜30 sec), then decanted, vacuumfiltered, washed with acetone 3 times, vacuum dried, and sifted through170 mesh. The information on the particulars of each Example is found inTable 5 below. The ammonium polyacrylate polymer in Examples 73 and 74may be sold as Dispex AA 4040.

Table 5 below shows at column 1, the “Example” number, at column 2, thesurfactant or other “Surface Agent” that was used. At column 3, whetheror not K₂HPO₄ was used (this column is labeled as “0.78M K₂HPO₄”. Ifthat column says Y, then 20 mL of 0.78M of K₂HPO₄ was used, if it saysN, then just 20 mL of water was used. Column 3 may also indicate otheradditives which are added along with the K₂HPO₄ or water, such as adding1 mL of 30% aqueous solution of H₂O₂. At column 4, which is labeled as“Amount”, lists whether the amount of “Surface Agent” used is 0.3 gramsor 0.3 mL. At column 5, the QE is shown. At column 6 is shown ΔQE, whichis the difference in QE between samples that included K₂HPO₄ and thosethat did not.

TABLE 5 0.78M Example Surface Agent K₂HPO₄ Amount QE ΔQE 54 97.6% 5519.8% 56 polyoxyethylene- Y 0.3 grams 64.4 polyoxypropylene blockcopolymer 57 polyoxyethylene- N 0.3 grams 26.9 37.5 polyoxypropyleneblock copolymer 58 polyoxyethylene- Y + 1 mL 0.3 grams 93.2polyoxypropylene block of 30% copolymer H₂O₂ (aq) 59 polyoxyethylene(20) Y 0.3 mL 90.8 sorbitan monolaurate detergent 60 polyoxyethylene(20) N 0.3 mL 21.8 69.0 sorbitan monolaurate detergent 61 Poly(acrylicacid sodium Y 0.3 grams 87.7 salt) 62 Poly(acrylic acid sodium N 0.3grams 75.6 12.1 salt) 63 Potassium sorbate Y 0.3 grams 88.4 64 Potassiumsorbate N 0.3 grams 43.7 44.6 65 EDTA Y 0.3 grams 95.9 66 EDTA N 0.3grams 97.7 1.8 67 Potassium citrate Y 0.3 grams 78.4 monohydrate 68Potassium citrate N 0.3 grams 96.2 17.8 monohydrate 69 Sodium Y 0.3grams 90.5 hexametaphosphate 70 Sodium N 0.3 grams 91.0 −0.5%hexametaphosphate 71 Polyvinylpyrrolidone Y 0.3 grams 83.2 72Polyvinylpyrrolidone N 0.3 grams 54.0 29.3 73 Ammonium polyacrylate Y0.3 mL 86.9 polymer 74 Ammonium polyacrylate N 0.3 mL 80.5 6.4 polymer75 sorbitan monooleate Y 0.3 grams 88.2 76 sorbitan monooleate Y 0.6grams 88.1

As shown above at column ΔQE, the average QE improvement by the use ofK₂HPO₄ was surprisingly 24.2%. Another observation is that H₂O₂increased QE by >25% as shown for Example 58. Moreover, many of thesurface agents also increased QE by a significant amount, as shown inTable 5.

Examples 77-86

For examples 77-84, 3.5 g of K₂SiF₆:Mn⁴⁺ was added to a solutioncontaining the surface agent listed at Table 6 in 15 mL of 0.39MK₂HPO₄(aq). The surface agent was provided in the amount listed in Table6 as well. The samples were roll milled for 30 minutes. The material wasthen allowed to settle, the supernatant decanted and the slurry wasvacuum filtered, rinsed once with 30 mL of H₂O+2 mL 30% H₂O₂, and then 5times with 40 mL of acetone before drying under vacuum. The driedsamples were then sieved through a 120 mesh nylon screen. Example 86 isthe mother batch used for examples 77-85 and was not subject to watertreatment. Example 85 was subject to water treatment but not to asurface agent. The results of the testing are shown at Table 6 with thefirst column giving the number of the Example, the second columnidentifying the surface agent used, the third column quantifying theamount of surface agent (“SA”) used, and the fourth column providing theQE of such sample. As Table 6 demonstrates, the effect of watertreatment on Example 85 significantly reduced QE. However, the additionof surface agents and K₂HPO₄ largely reversed the detrimental QE effectsshown at Example 85.

TABLE 6 Example Surface agent Amount of SA QE 77Ethylenediaminetetraacetic 0.2 g 93.4 acid dipotassium salt dihydrate 78Ethylenediaminetetraacetic 0.4 g 95.4 acid dipotassium salt dihydrate 79Ethylenediaminetetraacetic 0.2 g 99.0 acid dipotassium salt dihydrate 80Potassium citrate tribasic 0.2 g 93.5 monohydrate 81 Potassium citratetribasic 0.4 g 93.5 monohydrate 82 Potassium citrate tribasic 0.2 g 99.0monohydrate 83 Sodium 0.2 g 88.7 hexametaphosphate 84 Sodium 0.2 g 98.7hexametaphosphate 85 None (control) NA 18.8 86 None (mother batch) NA 97

Additional testing results on samples 77-86 are provided at Table 7below.

TABLE 7 D10/50/90 D10/50/90 (μm) no Span no (μm) with Span with Examplesonication sonication sonication sonication ΔD50 Δspan 77 6.6/9.5/130.67 3.7/5.1/6.6  0.57 4.4 0.11 78  8.4/14.6/26.9 1.27 6.9/9.3/12.4 0.595.3 0.68 79 5.1/7/9.4 0.61 3.7/5/6.5 0.56 2 0.05 80 10.2/11/37.4 2.475.4/7.2/9.6  0.58 3.8 1.89 81 10.1/18.4/32.2 1.20 5.3/7.1/9.4  0.58 11.30.62 82 10.2/21.9/43.8 1.53 6.8/9.3/12.6 0.62 12.6 0.91 8310.1/18.6/33.1 1.24 6.2/8.5/11.3 0.60 10.1 0.64 84  9.9/18.6/34.9 1.347.9/11.8/16.9  0.76 6.8 0.58 85 12.7/32.4/72.1 1.83 11/19.2/26.2 0.7913.2 1.04 86 11.1/26.6/59.2 1.81  9/13.6/20.2 0.82 13 0.98

At table 7, the first column is the Example number. The second columnshows the secondary particle sizes as measured without sonication. Thethird column shows the span with no sonication. Span measures the widthof the particle size distribution. In the third column, Examples 85 and86, which were not treated with surface active agents, showed arelatively large span. Except for Example 80, the examples with surfaceactive agents showed a decrease in span relative to Examples 85 and 86,which means that they showed better dispersion and less agglomerationsince the spread of particle sizes was narrower. In the fourth column isinformation on secondary particle size with sonication. In the fifthcolumn is information on the span for the samples with sonication. Evenwith sonication, which improves dispersion and reduces agglomeration,the samples with surface agents decreased the span relative to samples85 and 86, which shows the improvement in dispersion and the decrease inagglomeration. Column 6 shows the change in D50 (ΔD50) betweennon-sonication and sonication. The ΔD50 is also related to the degree ofdispersion and agglomeration since a greater ΔD50 means that thesonication had more of an effect on dispersion and agglomeration.Examples 85 and 86 had greater ΔD50 than all of the samples whichreceived surface agent treatment, which means that the examples with thesurface treatment improved dispersion and reduced agglomeration.

Examples 87-95 Example 87

Example 87 contained K₂SiF₆:Mn⁴⁺ without any stabilizing treatment andwhich was also not exposed to a water test. This is the control used inconjunction with examples 88-95.

Examples 88-95

Examples 88-95 were carried out to determine the effect of liquid waterexposure of K₂SiF₆:Mn⁴⁺ in the presence of AlPO₄. 1.2 g samples ofK₂SiF₆:Mn⁴⁺ was combined with, respectively, 3.6 mL of high puritydeionized water, 0.39 M K₂HPO₄, 0.39 M AlPO₄, 0.39 M AlPO₄ plus 0.3 mL30% H₂O₂, 0.1 M AlPO₄, 0.1 M AlPO₄ plus 0.3 mL 30% H₂O₂, 0.6 M AlPO₄,and 0.6 M AlPO₄ plus 0.3 mL of 30% H₂O₂. All samples were shaken brieflyto mix and rolled at 40 rpm for 1 hr. The pH of each sample was recordedand then each was filtered and washed three times with acetone (50 mLtotal). The filter cakes were collected and dried under vacuum in adesiccator overnight. High purity deionized water was then added to theisolated powders in a 1 g powder:3 g water ratio in a new plasticbottle. These samples were shaken briefly to mix and rolled at 40 rpmfor 1 hr. Each sample was filtered and washed three times with acetone(50 mL total) and the filter cakes were collected and dried under vacuumin a desiccator overnight. The results are shown in Table 8 below.

TABLE 8 pH after Example Description rolling QE QE drop 87 1.2 g PFS N/A102.5% N/A 88 1.2 g PFS + 3.6 mL high 2.87 39.4% 63.1% purity deionizedwater 89 1.2 g PFS + 3.6 mL 0.39M 7.76 99.7% 2.8% K₂HPO₄ 90 1.2 g PFS +3.6 mL 0.39M 1.68 99.3% 3.2% AlPO₄ 91 1.2 g PFS + 3.6 mL 0.39M 1.3486.1% 16.4% AlPO₄ + 0.3 mL 30% H₂O₂ 92 1.2 g PFS + 3.6 mL 0.1M 1.6064.5% 38.0% AlPO₄ 93 1.2 g PFS + 3.6 mL + 0.1M 1.38 75.6% 26.9% AlPO₄ +0.3 mL 30% H₂O₂ 94 1.2 g PFS + 3.6 mL + 0.6M 1.08 99.8% 2.7% AlPO₄ 951.2 g PFS + 3.6 mL + 0.6M 1.21 98.1% 4.4% AlPO₄ + 0.3 mL 30% H₂O₂

The results above are consistent with other Examples in which treatmentof K₂SiF₆:Mn⁴⁺ with water causes a huge drop in QE and the treatmentwith K₂HPO₄ significantly improves the QE. ΔQE is the difference betweenthe control (Example 87) and the remainder of the Examples (Examples88-95). As is clear from the above data, the QE drop with the use ofjust water (Example 88) was 63.1%. Surprisingly, all other examples hada much smaller reduction of QE. The largest decrease was 38.0% which isstill much smaller than the QE loss observed for Example 88. Thisfurther demonstrates the utility of the present invention in stabilizingphosphors against the detrimental effects of water. While exposure toK₂HPO₄ resulted in better QE values than AlPO₄, the treatment of bothAlPO₄ and H₂O₂ resulted in similar performance as K₂HPO₄ alone. However,AlPO₄ at 0.39 M and 0.6 M nonetheless resulted in very good QE valueseven without H₂O₂.

Examples 96-100

Examples 96-100 are directed towards the improvement of phosphorrobustness towards liquid water and water vapor upon treatment with MgF₂with and without potassium hydrogen phosphate treatment. The startingK₂SiF₆:Mn⁴⁺ phosphor powder had an average secondary d50 particle sizeof 12.3 μm as determined by light scattering.

Example 96

1 g of the starting K₂SiF₆:Mn⁴⁺ phosphor was mixed with 3 g deionizedwater in a 15 mL plastic bottle. The mixture was shaken by hand for 15seconds and then rolled at 40 rpm for 1 hour. The mixture was filteredon Whatman #4 filter paper and washed 4 times with a total of 100 mLacetone. The powder was dried under vacuum for 3 days.

Example 97

5 g of the starting phosphor of Example 96 was coated with MgF₂ usingthe amount of MgSiF₆.6H₂O precursor that produces MgF₂ in the amount of1% by weight with respect to the starting phosphor, according to theprocedure defined in Example 51. 1 g of the coated phosphor was mixedwith 3 g deionized water in a 15 mL plastic bottle. The mixture wasshaken by hand for 15 seconds and then rolled at 40 rpm for 1 hour. Themixture was filtered on Whatman #4 filter paper and washed 4 times witha total of 100 mL acetone. The powder was dried under vacuum for 3 days.

Example 98

5 g of the starting phosphor of Example 96 was coated with MgF₂ usingthe amount of MgSiF₆.6H₂O precursor that produces MgF₂ in the amount of1% by weight with respect to the starting phosphor, according to theprocedure defined in Example 51. After the residual HF solution wasfiltered off the product and rinsed 2× with acetone, the semi-dry cakewas transferred back into the reaction beaker. To this solid was added30 mL of 0.39M aqueous K₂HPO₄. The mixture was mixed at 140 rpm for 2minutes. The slurry was transferred to a fresh plastic Buchner funnelfitted with a 0.7 μm paper membrane (Whatman GF/F). The aqueous solutionwas filtered off. The solid was washed with acetone 4× and then driedunder vacuum. 1 g of this coated phosphor subsequently treated withK₂HPO₄ was mixed with 3 g deionized water in a 15 mL plastic bottle. Themixture was shaken by hand for 15 seconds and then rolled at 40 rpm for1 hour. The mixture was filtered on Whatman #4 filter paper and washed 4times with a total of 100 mL acetone. The powder was dried under vacuumfor 3 days.

Example 99

5 g of the starting phosphor of Example 96 was coated with MgF₂ usingthe amount of MgSiF₆.6H₂O precursor that produces MgF₂ in the amount of5% by weight with respect to the starting phosphor, according to theprocedure defined in Example 51. 1 g of the starting phosphor was mixedwith 3 g deionized water in a 15 mL plastic bottle. The mixture wasshaken by hand for 15 seconds and then rolled at 40 rpm for 1 hour. Themixture was filtered on Whatman #4 filter paper and washed 4 times witha total of 100 mL acetone. The powder was dried under vacuum for 3 days.

Example 100

5 g of the starting phosphor of Example 96 was coated with MgF₂ usingthe amount of MgSiF₆.6H₂O precursor that produces MgF₂ in the amount of5% by weight with respect to the starting phosphor, according to theprocedure defined in Example 51. After the residual HF solution wasfiltered off the product and rinsed 2× with acetone, the semi-dry cakewas transferred back into the reaction beaker. To this solid was added30 mL of 0.39M aqueous K₂HPO₄. The mixture was mixed at 140 rpm for 2minutes. The slurry was transferred to a fresh plastic Buchner funnelfitted with a 0.7 μm paper membrane (Whatman GF/F). The aqueous solutionwas filtered off. The solid was washed with acetone 4× and then driedunder vacuum. 1 g of this coated phosphor subsequently treated withK₂HPO₄ was mixed with 3 g deionized water in a 15 mL plastic bottle. Themixture was shaken by hand for 15 seconds and then rolled at 40 rpm for1 hour. The mixture was filtered on Whatman #4 filter paper and washed 4times with a total of 100 mL acetone. The powder was dried under vacuumfor 3 days.

After mixing the starting phosphor in water for 1 hour, the QE droppedfrom 99.9% to 16.8% as shown in Table 9 (Example 96). By comparison, thephosphor coated at the 1% MgF₂ level dropped down only to 77.6% (Example97), and the phosphor coated at the 5% MgF₂ level only dropped down to93.3% (Example 99). Incorporating treatment of the MgF₂-coated phosphorwith aqueous K₂HPO₄, by simply mixing the MgF₂-coated product with 0.39Maqueous K₂HPO₄ for 2 minutes, resulted in an even more significantpreservation of QE upon exposure to liquid water. When phosphor wascoated with MgF₂ at the 1% level and then mixed with aqueous K₂HPO₄, theQE dropped only 1.3% upon mixing with pure water for one hour. Alsoshown by the data in Table 9 is the fact that the drop in QE associatedwith exposure to 85% relative humidity at 85° C. for 100 hours was muchless with the MgF₂-coated phosphor particles compared to the startingphosphor. The QE drop upon exposure to humidity was reduced even furtherwhen the MgF₂-coated phosphor was treated with aqueous K₂HPO₄.

TABLE 9 QE after Secondary mixing in HTHH QE particle size QE before H₂Ofor one drop after Example (μm) H₂O mixing hour 100 h 96 12.3 99.9%16.8% 43.6% 97 8.8 99.5% 77.6% 30.3% 98 9.9 99.8% 98.5% 16.7% 99 10.899.6% 93.3% 19.4% 100 9.7 99.0% 99.7% 16.9%

As shown in Table 9, coating the phosphor with MgF₂ with and withoutsubsequent treatment with aqueous K₂HPO₄ has three benefits: it enhancesdispersibility, it enhances robustness against liquid water, and itenhances robustness against humidity at elevated temperature. Theseeffects are enhanced further still in compositions of the presentinvention wherein the phosphor coated with MgF₂ is subsequently treatedwith aqueous K₂HPO₄.

1. A process comprising combining a) a solution comprising at least onesubstance selected from the group consisting of: K₂HPO₄, an aluminumphosphate, oxalic acid, phosphoric acid, a surfactant, a chelatingagent, or a combination thereof, with b) a Mn⁴⁺ doped phosphor offormula I in solid form;A_(x)[MF_(y)]:Mn⁴⁺.   I and isolating a stabilized Mn⁴⁺ doped phosphorin solid form; wherein A is Li, Na, K, Rb, Cs, or a combination thereof,M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd, or acombination thereof, x is the absolute value of the charge of the[MF_(y)] ion; y is 5, 6 or
 7. 2. The process according to claim 1,further comprising, prior to combining with at the least one substance,contacting the Mn⁴⁺ doped phosphor of formula I with afluorine-containing oxidizing agent in gaseous form at an elevatedtemperature, to form a product phosphor.
 3. The process according toclaim 1, wherein M is Si, Ge, Ti, or a combination thereof, A is Na, K,or a combination thereof.
 4. The process according to claim 1, whereinthe phosphor of formula I is K₂SiF₆:Mn⁴⁺.
 5. The process according toclaim 1, wherein the at least one substance comprises K₂HPO₄.
 6. Theprocess according to claim 1, wherein the at least one substancecomprises the surfactant.
 7. The process according to claim 1, whereinthe at least one substance comprises the surfactant and K₂HPO₄.
 8. Theprocess according to claim 1, wherein the solution is aqueous andadditionally comprises H₂O₂.
 9. The process according to claim 6,wherein the solution additionally comprises at least one solventselected from the group consisting of: 1-octadecene, isonorbornylacrylate, water, and propylene glycol monomethyl ether acetate.
 10. Theprocess according to claim 1, wherein the at least one substancecomprises the surfactant, and wherein the surfactant comprises at leastone selected from the group consisting of: polyoxyethylene octyl phenylether, potassium oleate, polyoxyethylene-polyoxypropylene blockcopolymer; polyoxyethylene (20) sorbitan monolaurate, poly(acrylic acidsodium salt), and potassium sorbate.
 11. The process according to claim1, wherein the Mn⁴⁺ doped phosphor of formula I comprises a corecomprising a phosphor of formula I and a composite coating disposed onthe core, the composite coating comprising a metal fluoride selectedfrom the group consisting of calcium fluoride, strontium fluoride,magnesium fluoride, yttrium fluoride, scandium fluoride, lanthanumfluoride, and combinations thereof.
 12. A composition comprising a) atleast one substance selected from the group consisting of: K₂HPO₄, analuminum phosphate, oxalic acid, phosphoric acid, or a combinationthereof, and b) a Mn⁴⁺ doped phosphor of formula I;A_(x)[MF_(y)]:Mn⁴⁺   I wherein A is Li, Na, K, Rb, Cs, or a combinationthereof, M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd,or a combination thereof, x is the absolute value of the charge of the[MF_(y)] ion; y is 5, 6 or
 7. 13. The composition according to claim 12,wherein M is Si, Ge, Ti, or a combination thereof, A is Na, K, or acombination thereof.
 14. The composition according to claim 12, whereinthe phosphor of formula I is K₂SiF₆:Mn⁴⁺.
 15. The composition accordingto claim 12, wherein the at least one substance comprises K₂HPO₄ andmagnesium fluoride.
 16. The composition according to claim 12, whereinthe Mn⁴⁺ doped phosphor of formula I comprises a core comprising aphosphor of formula I and a manganese-free composite coating disposed onthe core, the manganese-free composite coating comprising a compound offormula III and a metal fluoride selected from the group consisting ofcalcium fluoride, strontium fluoride, magnesium fluoride, yttriumfluoride, scandium fluoride, lanthanum fluoride, and combinationsthereof,A¹ _(x)[M¹F_(y)]  (III) wherein A¹ is H, Li, Na, K, Rb, Cs, or acombination thereof, M¹ is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La,Nb, Ta, Bi, Gd, or a combination thereof, x is the absolute value of thecharge of the [M¹F_(y)] ion; and y is 5, 6 or
 7. 17. A display devicecomprising a stabilized Mn⁴⁺ doped phosphor produced by the processaccording to claim
 1. 18. The display device according to claim 17,wherein the display device comprises a television, a computer monitor, acellular or conventional phone, a digital photo frame, a tablet, anautomotive display, an e-book reader, an electronic dictionary, adigital camera, an electronic keyboard, or a gaming device.
 19. Alighting apparatus comprising a stabilized Mn⁴⁺ doped phosphor producedby the process according to claim
 1. 20. A phosphor compositioncomprising phosphor particles and comprising, on surfaces of thephosphor particles, at least one surface composition selected from thegroup consisting of: 1) a composition comprising a phosphorus-containingmoiety and a carbon-containing moiety; 2) a composition comprising thephosphorus-containing moiety and a metal fluoride; 3) a compositioncomprising the phosphorus-containing moiety and the carbon-containingmoiety and the metal fluoride; and 4) a composition comprising thephosphorus-containing moiety free of an alkyl phosphate compound,wherein the phosphor particles comprise a Mn⁴⁺ doped phosphor of formulaI;A_(x)[MF_(y)]:Mn⁴⁺   I wherein A is Li, Na, K, Rb, Cs, or a combinationthereof, M is Si, Ge, Sn, Ti, Zr, Al, Ga, In, Sc, Y, La, Nb, Ta, Bi, Gd,or a combination thereof, x is the absolute value of the charge of the[MF_(y)] ion; y is 5, 6 or
 7. 21. The phosphor composition according toclaim 20, wherein the metal fluoride comprises magnesium fluoride. 22.The phosphor composition according to claim 20, wherein thephosphorus-containing moiety comprises a phosphate moiety.
 23. Thephosphor composition according to claim 20, wherein thecarbon-containing moiety comprises at least one selected from the groupconsisting of: ethylenediaminetetraacetic acid, polyoxyethylene octylphenyl ether, potassium oleate, polyoxyethylene-polyoxypropylene blockcopolymer, polyoxyethylene (20) sorbitan monolaurate, poly(acrylic acidsodium salt), potassium sorbate, and derivatives or salts thereof. 24.The phosphor composition according to claim 20, wherein the phosphorparticles exhibit A) a quantum efficiency after exposure to liquid waterfor one hour at room temperature that is 50% to 100% of the quantumefficiency exhibited before water exposure or B) a quantum efficiencyloss upon exposure to 85% relative humidity at 85 deg C. for 100 hoursthat is less than 40%.
 25. The phosphor composition according to claim20, wherein a D₅₀ particle size of the phosphor particles beforesonication of a suspension containing the particles is no greater than30 μm and the D₅₀ particle size of the phosphor particles aftersonication is no greater than 20 μm.
 26. A display device comprising thephosphor composition according to claim
 20. 27. A light emitting diodedevice being radiationally coupled to and/or comprising the phosphorcomposition according to claim
 20. 28. The light emitting diode deviceaccording to claim 27, wherein the light emitting diode device is a miniLED or a micro LED.
 29. The light emitting diode device according toclaim 27, wherein a) the light emitting diode device comprises an LEDchip on which the phosphor composition is deposited and/or b) thecomposition is dispersed in a polymeric resin in a form of a film.